The fluxonium artificial atom
Abstract
Superconducting artificial atoms are all based on the purely
dispersive non-linearity of a Josephson tunnel junction, which provides
anharmonicity for a microwave oscillator mode. In the
fluxonium [1], the microwave oscillator crucially involves a
superinductor[2,3], built with a linear array of several tens of
“large” Josephson junctions. As the flux threading the loop formed by
the superinductor and the tunnel junction is swept from zero to half a
flux quantum, the ground-excited (g-e) transition frequency varies
between a sweet spot around 10GHz and another sweet spot at a few
hundreds of MHz. By optimizing the fabrication and parameters of this
superinductor, we have eliminated spurious phase slips through the
array, and ensured that its self-resonance frequency lies above the g-e
transition frequency. The improved relaxation times of this
multi-junction circuit, which can reach 0.001s, are promising for the
design of a novel mesoscopic artificial atom, in which large
anharmonicity, long coherence times and fast coupling rate to a cavity
bus would all be compatible.
[1] Manucharyan et al., Science, 326 (2009) and Phys. Rev. B 85, 024521 (2012).
[2] Masluk et al., Phys. Rev. Lett. 109, 137002 (2012).
[3] Bell et al., Phys. Rev. Lett. 109, 137003 (2012).